Good luck with it.
At 2 they are rather young so make sure they all have an adult with them.
Can you let them use a big ball pool, and a pile of soft toys for a short while. Then a singing session (if they go to a toddler group they may now the same songs). Can you borrow a big story book from the library (there are some that are big enough for all the children to see the pictures). Then while they are all sat quietly (!with luck!) hand out party food boxes.
Can parents bring boosters and closed drinkers for their children, otherwise you could have spills and chaos. It's not really a good time of year - outdoors might be easier.
Some Soft Play areas have a special part for young children, ours
http://www.cheshirefarmicecream.co.uk/crazy-daisys-play-barn/ also has rooms with small tables and chairs which they hire for party teas (you can bring food or buy platters from them). Or how about a visit to a petting farm.